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Spin fluctuations in α-Mn metal
385 SPIN FLUCTUATIONS IN a - M n METAL
H. N A G A S A W A * and S. M U R A Y A M A Physics Department of Tokyo University of Education, Ohtsuka, Tokyo, Japan
Temperature dependence of electrical resistivity in t~-Mn metal was measured below 4.2 K under an external magnetic field up to 100 kOe and the appreciable decrease of T 2 term in resistivity was found under high magnetic fields.
a - M n has a b.c.c, structure and contains four inequivalent crystallographic sites in unit cell. Neutron diffraction investigations [1] established the non-collinear spin ordering of a Mn below 95 K and determined the localized moments of 1.9, 1.7, 0.6, and 0.25/~a for a manganese atom in site I, II, III, and IV, respectively, at 4.4 K. These results are confirmed by recent NMR studies [2] below T N. The internal fields of 55Mn nuclei at each atomic site were found to correspond roughly to the magnetic moments determined by the neutron diffraction study. It is interesting to point out that large localized magnetic moments exist on the Mn atoms at site I and site II above TN as well below TN. In case of the paramagnetic state the observation of large negative-shifted NMR signal [3] which shows distinct temperature dependence, is attributed to Mn atoms at site ! and site II. On the other hand, the unshifted and temperature independent resonance line is due to Mn atoms at sites III and IV. These NMR results are consistent with the previous neutron diffraction study by Shull and Wilkinson [4]. They reported an average magnetic moment of 0.5 ~B in the paramagnetic phase up to about 500 K by using the diffuse scattering technique. But recent detailed magnetic susceptibility measurements [5] on the paramagnetic phase have been analyzed to yield an average moment of 2.37/~B and high Weiss temperature of 500 K, in contrasts to the neutron diffraction results. The existence of the large localized moment was verified recently by the high resolution Xray photo-emission spectra of paramagnetic t~Mn [6]. Multiplet splitting of the 3s and 2s lines reveals the presence, on the 10-15 s time scale, of a localized 3d spin, corresponding to a localized moment of 2.5 ~a. These results did not always
contradict the results of neutron scattering, because neutron scattering would detect moments with correlation times of 10-12s or longer. In other words, these experimental results seem to suggest that the localized magnetic moment of 2.5 ~a in paramagnetic a - M n at sites III and IV fluctuates rapidly in a period of 10-14 s (hi500 K). On the other hand, a - M n is remarkable for the exceptionally high value of the coefficient of the T 2 term in resistivity below 20 K, known as the largest in pure metal and about four orders of magnitude larger than that in P d [7]. On the basis of the experimental results given above and the theoretical discussion on resistivity due to dilute magnetic impurities [8] and in weakly ferromagnetic metals [9], it may be naturally concluded that the anomalously large coefficient
* Present address: Institute for Physics, The University of Tsukuba, Ibaragi, Japan.
Fig. 1. Temperature dependence of transverse magnetoresistance in a-Mn.
Physica 86--88B (1977) 385-386 © North-Holland
5
J I
1-
32 J
30
28
S
T2(KT)
386 o f the T 2 t e r m o f r e s i s t i v i t y in a - M n o r i g i n a t e s from spin fluctuations. In o r d e r to o b t a i n f u r t h e r k n o w l e d g e o f spin f l u c t u a t i o n a - M n m e t a l a n d its a l l o y s , w e h a v e measured the temperature dependence of elect r i c a l r e s i s t i v i t y o f a - M n u n d e r a large e x t e r n a l m a g n e t i c field. W e f o u n d t h a t the coefficient of t h e T 2 t e r m in r e s i s t i v i t y at l o w t e m p e r a t u r e d e c r e a s e s a p p r e c i a b l y u n d e r m a g n e t i c field up to 100 k O e as s h o w n in fig. 1. T h e s e r e s u l t s s u g g e s t t h a t spin f l u c t u a t i o n in a n t i - f e r r o m a g n e t i c a - M n m e t a l m a y b e s u p p r e s s e d b y large a p p l i e d m a g netic fields.
References [1] J.S. Kasper and B.W. Robert, Phys. Rev. 101 (1956) 537. T. Yamada, N. Kunitomi, Y. Nakai, D.E. Cox and G. Shirane, J. Phys. Soc. Jap. 28 (1970) 615.
[2] H. Yamagata and K. Asayama, J. Phys. Soc. Japan. 33 (1972) 400. [3] V. Jaccarino and J.A. Seitchik, Bull. Amer. Phys. Soc. 10 (1965) 317. [4] C.G. Shull and M.K. Wilkinson, Rev. Mod. Phys. 25 (1953) 100. [5] H. Nagasawa and M. Uchinami, Phys. Lett. 42A (1973) 463. [6] F.R. McFeely, S.P. Kowalczyk, L. Ley and D.A. Shirley, Solid State Commun. 15 (1974) 1051. [7] H. Nagasawa and M. Senba, J. Phys. Soc. Jap. 39 (1975) 70. [8] P. Lederer and D.L. Mills, Phys. Rev. 165 (1968) 837. [9] K. Ueda and T. Moriya, J. Phys. Soc. Jap. 39 (1975) 605.
H. N A G A S A W A * and S. M U R A Y A M A Physics Department of Tokyo University of Education, Ohtsuka, Tokyo, Japan
Temperature dependence of electrical resistivity in t~-Mn metal was measured below 4.2 K under an external magnetic field up to 100 kOe and the appreciable decrease of T 2 term in resistivity was found under high magnetic fields.
a - M n has a b.c.c, structure and contains four inequivalent crystallographic sites in unit cell. Neutron diffraction investigations [1] established the non-collinear spin ordering of a Mn below 95 K and determined the localized moments of 1.9, 1.7, 0.6, and 0.25/~a for a manganese atom in site I, II, III, and IV, respectively, at 4.4 K. These results are confirmed by recent NMR studies [2] below T N. The internal fields of 55Mn nuclei at each atomic site were found to correspond roughly to the magnetic moments determined by the neutron diffraction study. It is interesting to point out that large localized magnetic moments exist on the Mn atoms at site I and site II above TN as well below TN. In case of the paramagnetic state the observation of large negative-shifted NMR signal [3] which shows distinct temperature dependence, is attributed to Mn atoms at site ! and site II. On the other hand, the unshifted and temperature independent resonance line is due to Mn atoms at sites III and IV. These NMR results are consistent with the previous neutron diffraction study by Shull and Wilkinson [4]. They reported an average magnetic moment of 0.5 ~B in the paramagnetic phase up to about 500 K by using the diffuse scattering technique. But recent detailed magnetic susceptibility measurements [5] on the paramagnetic phase have been analyzed to yield an average moment of 2.37/~B and high Weiss temperature of 500 K, in contrasts to the neutron diffraction results. The existence of the large localized moment was verified recently by the high resolution Xray photo-emission spectra of paramagnetic t~Mn [6]. Multiplet splitting of the 3s and 2s lines reveals the presence, on the 10-15 s time scale, of a localized 3d spin, corresponding to a localized moment of 2.5 ~a. These results did not always
contradict the results of neutron scattering, because neutron scattering would detect moments with correlation times of 10-12s or longer. In other words, these experimental results seem to suggest that the localized magnetic moment of 2.5 ~a in paramagnetic a - M n at sites III and IV fluctuates rapidly in a period of 10-14 s (hi500 K). On the other hand, a - M n is remarkable for the exceptionally high value of the coefficient of the T 2 term in resistivity below 20 K, known as the largest in pure metal and about four orders of magnitude larger than that in P d [7]. On the basis of the experimental results given above and the theoretical discussion on resistivity due to dilute magnetic impurities [8] and in weakly ferromagnetic metals [9], it may be naturally concluded that the anomalously large coefficient
* Present address: Institute for Physics, The University of Tsukuba, Ibaragi, Japan.
Fig. 1. Temperature dependence of transverse magnetoresistance in a-Mn.
Physica 86--88B (1977) 385-386 © North-Holland
5
J I
1-
32 J
30
28
S
T2(KT)
386 o f the T 2 t e r m o f r e s i s t i v i t y in a - M n o r i g i n a t e s from spin fluctuations. In o r d e r to o b t a i n f u r t h e r k n o w l e d g e o f spin f l u c t u a t i o n a - M n m e t a l a n d its a l l o y s , w e h a v e measured the temperature dependence of elect r i c a l r e s i s t i v i t y o f a - M n u n d e r a large e x t e r n a l m a g n e t i c field. W e f o u n d t h a t the coefficient of t h e T 2 t e r m in r e s i s t i v i t y at l o w t e m p e r a t u r e d e c r e a s e s a p p r e c i a b l y u n d e r m a g n e t i c field up to 100 k O e as s h o w n in fig. 1. T h e s e r e s u l t s s u g g e s t t h a t spin f l u c t u a t i o n in a n t i - f e r r o m a g n e t i c a - M n m e t a l m a y b e s u p p r e s s e d b y large a p p l i e d m a g netic fields.
References [1] J.S. Kasper and B.W. Robert, Phys. Rev. 101 (1956) 537. T. Yamada, N. Kunitomi, Y. Nakai, D.E. Cox and G. Shirane, J. Phys. Soc. Jap. 28 (1970) 615.
[2] H. Yamagata and K. Asayama, J. Phys. Soc. Japan. 33 (1972) 400. [3] V. Jaccarino and J.A. Seitchik, Bull. Amer. Phys. Soc. 10 (1965) 317. [4] C.G. Shull and M.K. Wilkinson, Rev. Mod. Phys. 25 (1953) 100. [5] H. Nagasawa and M. Uchinami, Phys. Lett. 42A (1973) 463. [6] F.R. McFeely, S.P. Kowalczyk, L. Ley and D.A. Shirley, Solid State Commun. 15 (1974) 1051. [7] H. Nagasawa and M. Senba, J. Phys. Soc. Jap. 39 (1975) 70. [8] P. Lederer and D.L. Mills, Phys. Rev. 165 (1968) 837. [9] K. Ueda and T. Moriya, J. Phys. Soc. Jap. 39 (1975) 605.